Herrmann R G, Steppuhn J, Herrmann G S, Nelson N
Botanisches Institut, Ludwig-Maximilians-Universität, München, Germany.
FEBS Lett. 1993 Jul 12;326(1-3):192-8. doi: 10.1016/0014-5793(93)81789-3.
Proton-translocating F-ATP synthases from chloroplasts contain a nuclear-coded subunit, CFo-II, that lacks an equivalent in the corresponding E. coli complex. Three recombinant phages that code for the entire precursor of this subunit have been isolated from lambda gt11 cDNA expression libraries made from polyadenylated spinach RNA using a two-step strategy. The reading frame of 222 amino acid residues includes 147 residues for the mature protein (M(r) 16.5 kDa) and a transit sequence of 75 residues (M(r) 8.0 kDa). Secondary structure predictions indicate a bitopic protein, anchored by a single N-terminal transmembrane segment and a C-terminal hydrophilic region that probably reaches into CF1. CFo-II precursor made in vitro can be imported into isolated, intact chloroplasts and assembled into ATP synthase. This protein is a real subunit of the plastid enzyme and a distinctive characteristic of ATP synthases involved in photosynthetic processes. Unique features are (i) that the gene for CFo-II (atpG) appears to be a duplication of atpF encoding CFo-I, the homologues of the genes for subunits b' and b in photosynthetic bacteria, (ii) that it represents the first instance that one copy of the various duplicated loci found in plastid chromosomes has been phylogenetically translocated to the nucleus, and (iii) that it operates with a bipartite (import/thylakoid-targeting) transit peptide but without an intermediate cleavage site for the stroma protease, suggestive of a way of membrane integration different from that of its plastome-encoded counterpart CFo-I. With these data, the first complete sequence for a chloroplast ATP synthase of a higher plant (spinach) is available.
叶绿体中的质子转运F-ATP合酶含有一个核编码亚基CFo-II，而在相应的大肠杆菌复合体中没有与之对应的亚基。使用两步策略，从由聚腺苷酸化菠菜RNA构建的λgt11 cDNA表达文库中分离出了三个编码该亚基完整前体的重组噬菌体。222个氨基酸残基的阅读框包括147个成熟蛋白残基（分子量16.5 kDa）和一个75个残基的转运序列（分子量8.0 kDa）。二级结构预测表明这是一种双位蛋白，由单个N端跨膜片段和可能伸向CF1的C端亲水区域锚定。体外合成的CFo-II前体可以导入分离的完整叶绿体中，并组装成ATP合酶。该蛋白是质体酶的一个真正亚基，也是参与光合过程的ATP合酶的一个独特特征。独特之处在于：（i）CFo-II（atpG）基因似乎是编码CFo-I的atpF的重复，CFo-I是光合细菌中b'和b亚基基因的同源物；（ii）它代表了质体染色体中发现的各种重复基因座的一个拷贝在系统发育上转移到细胞核的第一个实例；（iii）它通过一个双功能（导入/类囊体靶向）转运肽起作用，但没有基质蛋白酶的中间切割位点，这表明其膜整合方式与其质体基因组编码的对应物CFo-I不同。有了这些数据，就可以获得高等植物（菠菜）叶绿体ATP合酶的第一个完整序列。
